SECONDARY FAILURE RATES OF MEASLES-VACCINES - A METAANALYSIS OF PUBLISHED STUDIES

Background. Recent measles outbreaks in highly vaccinated populations have highlighted the role of vaccine failure as a barrier to the elimi nation of measles, We sought to estimate the rate of secondary failure (clinical measles after vaccine-induced seroconversion) of measles va ccines using metaanalysis. Methods. We identified 1411 studies of whic h 125 were relevant, From these we found 10 original studies of health y subjects with sufficient details to calculate a pooled secondary fai lure rate. We performed a test for homogeneity before any pooling. Res ults. Although significant heterogeneity prevented their pooling as a single group, the studies fell into three homogeneous groups suitable for pooling, Group A studies used killed vaccine whereas the other two groups (Groups B and C) of studies used live vaccine. These latter gr oups differ in that the studies in Group B share higher failure rates and are difficult to interpret with respect to the lack of verificatio n of vaccination, immunization before 12 months of age and a non-North American study site and vaccine manufacturer. Those studies in Group C, in which US subjects were older than 12 months at vaccination and r eceived a live US-manufactured vaccine that was documented in a medica l record, had a failure rate of 0 of 2031 with a 95% confidence interv al of 0.0 to 0.147%. Conclusions. Although reports of measles related to secondary failure exist, studies that permit the calculation of the rate of secondary failure demonstrate that the rate appears to be <0. 2%.